This application claims priority of United Kingdom patent Application 0000511.6, filed on Jan. 12, 2000.
The present invention is concerned with LED packages, particularly with LED packages which can serve as replacements for filament bulbs.
In many contexts, filament bulbs are being replaced by light emitting diodes (the abbreviation xe2x80x9cLEDxe2x80x9d will be used throughout this document in place of xe2x80x9clight emitting diodexe2x80x9d). To this end it is frequently necessary to provide an LED package which can be plugged directly into an existing socket intended to receive a filament bulb. Some packages having exterior dimensions and contact arrangements compatible with the existing sockets are known.
However, there is pressure to simplify the construction of such packages for the sake of economy. There are also difficulties in manufacturing small enough LED packages for use in certain contexts, such as replacements for miniature indicator bulbs.
In accordance with the present invention there is an LED package having a generally tubular electrically conductive body, a circuit board which is mounted across the body at or adjacent one end thereof. The circuit board has an outer face on which an LED is mounted. The LED package also having an end contact exposed at the end of the body remote from the circuit board and located relative to the body by means of an insulating cap mounted across the body. An electrical conductor extends from the end contact through the cap, through the interior of the body and through the circuit board to connect the end contact to one of the anode and the cathode of the LED. An electrically conductive path formed on the circuit board connects the other of the anode and the cathode of the LED to the body, such that the body serves as a second contact enabling current to be supplied to the LED.
This construction makes possible a compact LED package that is straightforward to manufacture. The shape and dimensions of the body and contact may be chosen such that the package can be inserted into existing sockets used for filament bulbs.
It is particularly preferred that the electrical conductor is connected to the LED through a connection pad formed on the circuit board""s outer face in a region beneath the LED. This makes possible particularly straightforward assembly of the package.
It is also preferred that the electrical conductor comprises a wire end inserted into a through going, plated hole in the circuit board whereby connection is made through the circuit board. This is constructionally straightforward.
The electrical conductor preferably comprises a resistor disposed within the body and connected between the end contact and the LED. This can serve to limit current through the LED and can be chosen to enable the package to operate at the supply voltage used for filament bulbs.
In alternative embodiments, the resistor can be replaced by, or connected to, an integrated circuit (xe2x80x9cICxe2x80x9d) or rectifier network. Such embodiments enable closer control of the current. Preferably the IC or rectifier network is chosen to allow the LED package to be operated independently of the polarity of the voltage supply or to be operated on an A.C. voltage dagger.
In an especially preferred embodiment of the present invention, a shoulder is formed in the vicinity of an end of the body and the circuit board is mounted with its inner face against the shoulder, the electrically conductive path from the LED to the body comprising a track on the circuit board leading from a portion of the inner face of the circuit board which lies against the shoulder, via a through-going plated hole in the circuit board to a solder fillet on the circuit board""s outer surface, the solder fillet connecting to the LED.
The LED and upper face of the circuit board may be encapsulated by a meniscus lens.
The present invention is particularly well suited to miniature LED packages, typically of the order of 5 to 10 mm in length.